1. Field of the Invention:
This invention relates to oil and to gas production equipment and, specifically, to improvements in oil and gas separators of the type utilizing float actuated pilot valves for controlling the discharge from the separator.
2. Description of the Prior Art:
It is well known that the flow stream from a petroleum well contains oil and gas portions with the gas portion remaining in solution in the liquid at well pressures. It is also known that if the liquid having these gaseous constituents in solution is opened to the atmosphere that the gases will come out of solution. Oil and gas separators are thus provided for gradually reducing the pressure on the petroleum liquid produced, thereby allowing the evolved gases to be taken away or removed from contact with the liquid. The remaining liquid can be separated into water and oil portions and the oil so produced will constitute a greater volume and increased yield than when the petroleum flow from the well is "flashed" to the atmosphere.
A typical oil and gas separator includes a tank or vessel having a input line for receiving the petroleum flow from the well and having a gas outlet at the top and a liquid discharge outlet at the bottom of the vessel. A liquid level controller is provided which uses a "float" or displacement type sensor to transmit changes in the liquid level in the tank to a pilot valve outside the vessel. The pilot valve in turn, signals a discharge valve in the discharge outlet from the vessel to open or close the discharge valve in response to the liquid level within the vessel.
In the past, pilot valves associated with the float type controller have generally been operated pneumatically, utilizing a supply gas pressure taken from the production gas. When the liquid level in the vessel was within the desired limit, the supply gas was vented through the pilot valve to the atmosphere. When the liquid level rose sufficiently and changed the position of the float, the supply gas was diverted within the pilot valve to thereby provide a control signal to the discharge valve to allow liquid to flow from the vessel.
Such float controller and pilot valve devices are known as "constant bleed control" devices in the industry and are straightforward and reliable controllers for oil and gas separators. However, since the supply signal gas is bled to the atmosphere until the liquid level reaches a predetermined limit within the separator, a certain amount of energy is wasted which could be recovered. A typical constant bleed control device consumes supply gas at a rate in the neighborhood of 350,000 standard cubic feed per year. It would be desirable in terms of energy conservation and depletion of natural resources to recover or prevent the waste of the supply gas which is bled to the atmosphere in presently existing bleed control devices.